1. Field of the Invention
The invention is a device for signaling to a vehicle driver an udner-inflated condition in a tire.
2. Description of the Prior Art
Under-inflation of tires on passenger cars, trucks and other vehicles causes poor fuel economy by increasing rolling resistance, shortened tire life by increasing heat build-up, and a greater chance of accidents by decreasing the handling capabilities of the vehicle. This leads to unnecessary loss of life and injury to persons and property.
While tires today are manufactured for dependability and durability, leakage of air through and around the valve stem and bead seat is unavoidable. Because of the current trend toward self-service gas stations, a vehicle owner often must check and maintain proper tire inflation himself, or take the risks assocated with under-inflation. Because many drivers lack either the knowledge, time or motivation to check and maintain proper tire pressure, a passive device is needed which will inform a driver of a low pressure condition in a tire without his making a conscious effort to detect the condition. Ideally, such a device would also offer the driver motivation to correct a low pressure condition by, for example, persistently signaling to the driver until tire pressure is raised to the proper level. To achieve the greatest possible fuel economy, such a device should be sensitive to a small pressure drop of about 5 psig. Finally, the device should be easily installed on wheels already in use and should not interfere with tire mounting or weaken the structure of the tire. Since a single vehicle's underinflated tire will undermine the safety of all surrounding persons and property, as well as contribute to fuel shortages felt by all, a cost low enough to ensure widespread use of the device is essential.
Prior art devices have not generally met these standards. Active valve stem indicators detect only gross changes in tire pressure and require an effort by a driver who must make a visual observation of a gauge. A driver can easily forget to check the gauge or ignore its indication of low pressure, in which case the device does not achieve its purpose.
Electronic low pressure indicators have been proposed, but would be too costly for widespread use by the driving public.
Low pressure warning devices which detect deformation in a tire's side wall interfere with the integrity of a tire's structure, are not easily installed on tires already in use, and make tire mounting difficult.